The present invention relates to an illumination optical system which converts randomly-polarized light into particular linearly-polarized light for illuminating a liquid crystal panel and the like, and a projection display apparatus incorporating the illumination optical system.
FIG. 15 is a horizontal sectional view showing a basic configuration of an illumination optical system of a conventional projection display apparatus, and FIG. 16 is a horizontal sectional view showing an enlarged view of a part of FIG. 15. As shown in FIG. 15 or FIG. 16, the conventional projection display apparatus comprises a light source 1, a first multi-lens array 9 configured by an arrangement of multiple first lens cells 9a, a second multi-lens array 3 configured by an arrangement of multiple second lens cells 3a, a polarization conversion module 4 configured by an arrangement of multiple polarization conversion units 4a, a condenser lens 5, a liquid crystal panel 6 as an optical modulation device, and a projection lens 7. In the projection display apparatus, the first lens cells 9a correspond to the polarization conversion units 4a in a one-to-one relationship, in a horizontal direction 10 orthogonal to a system optical axis 8. Multiple secondary light source images formed by the first multi-lens array 9 are converged in the vicinity of the second multi-lens array 3. The randomly-polarized light passing the second multi-lens array 3 is converted to linearly-polarized light by the polarization conversion module 4 and directed through the condenser lens 5 onto the liquid crystal panel 6. The light passing the liquid crystal panel 6 is modulated in accordance with a video signal input to the liquid crystal panel 6, and the projection lens 7 provides an enlarged projection on the screen (not shown).
However, it has been difficult to downsize the illumination optical system (and downsize the projection display apparatus) and to enhance the brightness of the display image hand in hand, with the conventional projection display apparatus as described above.
One reason that makes downsizing difficult is that a reduction in a distance L6 (a distance from the second multi-lens array 3 to the liquid crystal panel 6) in FIG. 15 is not allowed in many cases because of the constraints that optical components such as a reflecting mirror must be placed.
In addition, a reason that makes it difficult for the downsizing and the enhancement of the brightness to be compatible is that a reduction in a distance L9 (a distance from the first multi-lens array 9 to the second multi-lens array 3) in FIG. 15 increases the incident angle of the light incident to the opening 4b (width H4/2) of the polarization conversion unit 4a, consequently degrading the intensity of the transmission light (and reflection light). In this connection, FIG. 17 shows a relationship between the incident angle of the polarization conversion unit 4a and the transmittance (and reflectivity) of the transmission light (and reflection light) (that is, incident angle characteristics). Here, the incident angles are the angles xcex80 and xcex81 of the incident light beams (straight-line segments 11 and 12) with respect to the reference line 13 which is at a 45xc2x0 angle with respect to the polarization separation surface 4e of the polarization conversion unit 4a, as shown in the horizontal sectional view of FIG. 18 and its enlarged view of FIG. 19. As shown in FIG. 17, as a difference between the incident angle and a reference angle 0xc2x0 increases, the intensity of the incident light (and reflection light) decreases.
Furthermore, another reason that makes it difficult for the downsizing and the enhancement of the brightness to be compatible is that if the width H9 of the first lens cell 9a is reduced while maintaining a conjugated relationship between the first lens cell 9a and the liquid crystal panel 6 (relationship expressed as H6/H9=L6/L9) when reducing the distance L9 in FIG. 15, the width H4/2 of the opening 4b of the polarization conversion unit 4a must also be reduced, which would consequently demand a further high assembly precision and increase the risk of reduction in the amount of incident light (amount of light that can pass the opening 4b) owing to an assembly error.
It is an object of the present invention to provide a compact illumination optical system that can irradiate an area to be irradiated with a high intensity and a compact projection display apparatus that can provide a highly bright display image.
According to one aspect of the present invention, an illumination optical system comprises a first multi-lens array which includes a plurality of first lens cells, the first multi-lens array dividing incident light to form plurality of light beams and condensing each light beam, thereby forming a plurality of images; a second multi-lens array which includes a plurality of second lens cells, the second lens cells converging the plurality of images, respectively; and a polarization conversion module which includes an arrangement of a plurality of polarization conversion units, each polarization conversion unit converting randomly-polarized light into particular linearly-polarized light, a predetermined area being irradiated with the plurality of light beams which are generated by passing the incident light through the first multi-lens array, the second multi-lens array, and the polarization conversion module, wherein number of the first lens cells is greater than number of the polarization conversion units in a direction of the arrangement of the polarization conversion units; wherein each of particular ones among the polarization conversion units corresponds to at least two first lens cells in the direction of the arrangement of the polarization conversion units; wherein the first lens cell in a portion where each of the particular ones among the polarization conversion units corresponds to at least two first lens cells has such a decentered shape that a vertex of the first lens cell is off a center position of the first lens cell and closer to an incident axis passing a center of an opening of the corresponding polarization conversion unit.
In the illumination optical system, the width of the first lens cell is smaller than that of the conventional one, and the size of the image is also smaller than the size of the conventional one. Accordingly, the ratio of light incident to the opening of the polarization conversion unit of the polarization conversion module can be increased to enhance the utilization factor of light. In addition, the first lens cell has such a decentered shape that the vertex is off the center position of the first lens cell and closer to the incident axis passing the center of the opening of the corresponding polarization conversion unit, so that the incident angle of pencils of light incident to the polarization conversion unit can be brought closer to 0xc2x0, increasing the amount of light that passes the polarization conversion unit. Accordingly, the illumination optical system can enhance the intensity of light on the surface to be irradiated.
In addition, because the width of the first lens cell is smaller than the width of the polarization conversion unit in the illumination optical system, the distance from the first multi-lens array to the second multi-lens array can be reduced, so that the illumination optical system can be downsized.
Further, according to another aspect of the present invention, a projection display apparatus comprises a light source; a first multi-lens array which includes a plurality of first lens cells, the first multi-lens array dividing incident light to form plurality of light beams and condensing each light beam, thereby forming a plurality of images; a second multi-lens array which includes a plurality of second lens cells, the second lens cells converging the plurality of images, respectively; a polarization conversion module which includes an arrangement of a plurality of polarization conversion units, each polarization conversion unit converting randomly-polarized light into particular linearly-polarized light; and an optical modulation device being irradiated with the plurality of light beams which are generated by passing the incident light through the first multi-lens array, the second multi-lens array, and the polarization conversion module; wherein number of the first lens cells is greater than number of the polarization conversion units in a direction of the arrangement of the polarization conversion units; wherein each of particular ones among the polarization conversion units corresponds to at least two first lens cells in the direction of the arrangement of the polarization conversion units; wherein the first lens cell in a portion where each of the particular ones among the polarization conversion units corresponds to at least two first lens cells has such a decentered shape that a vertex of the first lens cell is off a center position of the first lens cell and closer to an incident axis passing a center of an opening of the corresponding polarization conversion unit.
Further, because the width of the first lens cell in the projection display apparatus is smaller than the width of the conventional one, the size of the image also becomes smaller than the conventional one. Accordingly, the ratio of light incident to the opening of the polarization conversion unit of the polarization conversion module can be increased to enhance the utilization factor of light. In addition, the first lens cell has such a decentered shape that the vertex is off the center position of the first lens cell and closer to the incident axis passing the center of the opening of the corresponding polarization conversion unit, so that the incident angle of pencils of light incident to the polarization conversion unit can be brought closer to 0xc2x0, increasing the amount of light that passes the polarization conversion unit. Accordingly, the projection display apparatus can enhance the brightness of the display image.
Furthermore, because the width of the first lens cell is smaller than the width of the polarization conversion unit in the projection display apparatus, the distance from the first multi-lens array to the second multi-lens array can be reduced, so that the projection display apparatus can be downsized.